A Brooklyn bus was evacuated yesterday after a passenger spotted an unattended bag near the back door – only days after cops began boarding buses and trains to remind passengers to report all suspicious packages in the wake of the London terror bombings.

The bag turned out to contain nothing but personal items, police said.

The B63 bus had reached the intersection of Fifth Avenue and 10th Street in Park Slope at around 6:45 p.m. when the passenger, whose identity was not released by police, spotted the bag and alerted the driver.

Within seconds, the driver cleared the bus and called his dispatcher, who called 911.

Police were on the scene in minutes, clearing the area for Emergency Service cops and the bomb squad, police said.

But within an hour, it was determined the duffel bag contained no explosives.

Police Commissioner Ray Kelly singled out a Harlem police sergeant who boarded a bus on the morning of the London attacks and lectured riders on what to look for.

Kelly said other officers would follow Sgt. Luis Piñero’s lead, telling riders to keep a sharp eye out for passengers who are nervous, appear overdressed and possibly hiding a bomb under unnecessary clothing, or sweating on an air-conditioned bus.